There are many dock board systems which have a mechanical arrangement for raising and lowering thereof and generally include a mechanical lock arrangement for locking the dock board in a particular position. Unfortunately, the loads exerted on the dock boards, and hence on the mechanical arrangements, change and, in particular, change due to the variable load or support the trailer bed exerts on the dock board as the trailer is being loaded or unloaded.
Problems occur when a trailer is unloaded in that the suspension of the trailer tends to raise the bed of the trailer and the dock board. The mechanical lock arrangement of the locked dock board tries to oppose this upward force and movement. This can result in very high loads on the dock board and causes high wear and deterioration of the mechanical lock. These lock mechanisms also become progressively more difficult to release as the load on the dock board increases and can lead to operator injury. The release problem is more acute if high upward loads are present, such as when a trailer is unloaded.
The unloading or loading of trailers typically involves a fork lift truck or other device which weighs 3000 to 5000 lbs. or more without the weight of the product. This causes the dock board and trailer to go down when the fork lift truck crosses the dock board, and the dock board and trailer should go up when the fork lift truck crosses over the dock board from the trailer. Thus, the forces exerted on the dock board vary widely during use.
Many mechanical dock board systems, as opposed to powered hydraulically controlled dock boards (having pumps and electrically controlled valves), are used in factories as they are generally less expensive and, typically, the owner of the building is not responsible for maintenance of the dock boards. This responsibility is typically the responsibility of the tenant renting the premises.
There remains a need for a simple arrangement for effectively locking the manual mechanical type dock boards in various positions while accommodating the variable forces thereon.
The present invention is directed to nonpowered, manual mechanical type dock boards and is not directed to powered hydraulic dock boards which are many times more expensive and require power at the dock board.